Electric motors are used for a multitude of tasks and frequently those motors are used in applications where cooling of the motor is difficult. Commonly, these hard-to-cool applications involve large motors. One example of a hard-to-cool application is a motor powering a dry-pit submersible or an explosion-proof submersible motor. Many other hard-to-cool applications exist and the present disclosure is not limited to submersible motors. In the past these hard-to-cool applications utilized motors that were oversized for the application or placed in an enclosure that did not offer as much protection as a totally enclosed motor. These oversized motors are more expensive to purchase.
Electric motors are used in environments that although aggressive to the motor components, the motors are placed there because of the superior cooling provided in such environments. For instance, hermetic motors are integrated into the motor-compressor system where the electrical package of the motor, i.e., the rotor and stator, is exposed to the refrigerant. These motors achieve superior cooling because the refrigerant is cool and/or the refrigerant evaporates directly on the motor surfaces, thus cooling them, but the refrigerant is aggressive towards, and damaging to, the winding.
Heat pipes, generally, are a heat transfer mechanism that can transport large quantities of heat with a very small difference in temperature between hot and cold interfaces. A typical heat pipe consists of sealed hollow tube made of a thermoconductive metal such as copper or aluminum. The pipe contains a relatively small quantity of a “working fluid” or coolant (such as water, ethanol or mercury) with the remainder of the pipe being filled with vapor phase of the working fluid, all other gases being excluded. Internally, in order to overcome gravitational forces (or because of their absence in the case of space applications) most heat pipes contain a wick structure. This typically consists of metal powder sintered onto the inside walls of the tube, but may, in principle, be any material capable of soaking up the coolant.